It makes more sense if you think about it as something that they need to do in order to make sure that their marketplace attracts a wide range of publishing com

It makes more sense if you think about it as something that they need to do in order to make sure that their marketplace attracts a wide range of publishing companies, some of which have very different perspectives on digital piracy, than as a way for them to retain a small percentage of revenue that DRM could theoretically protect.